Using a new antibody directed solely against the GABA molecule itself and receptor binding autoradiography, the long term objective of this proposed study is to determine the organization and function of GABAergic circuitry in specific neural regions of the autonomic nervous system, which are involved in regulation and/or modulation of cardiovascular and respiratory functions. The specific aims of this proposal include: 1) to investigate thoroughly at the light microscopic level in the cat immunohistochemical distribution of GABA containing neurons, fibers and terminals in the following autonomic nervous system nuclei: the nucleus tractus solitarii and the rostral ventral medullary area (of Schlaefke); 2) to study the transmitter coded circuitry of the GABAergic system at the ultrastructural level in the nucleus tractus solitarii and the rostral ventral medullary area (of Schlaefke) in order to determine the specific patterns of synaptic circuits concerning the localization of GABA receptors using (3H) muscimol in tractus solitarii and the rostral ventral medullary area of Schlaefke. The results of these studies will provide the first immunohistochemical and receptor binding evidence of the specific GABAergic circuits involved in autonomic nervous system nuclei. In addition, these studies will furnish an understanding of the neurobiology of GABAergic neurons which will contribute important information concerning the cells and circuits that are centrally involved in the regulation of cardiovascular and respiratory events such as blood pressure, heart rate and respiratory depression.